The invention relates to the synthesis of thiophene-based core perylene diimide tetramers, hexamers, octamers or higher oligomers via a unique direct heteroarylation (DHA). Certain thiophene-based core structures are functionalized with four or more perylene diimides at active C—H positions in the core. The methods herein provide simple synthetic pathways to tetrameric and higher oligomeric perylene diimides, which are useful, at least, as electron acceptors for organic solar cells. The invention further relates to the PDI tetramers, hexamers, octamers and higher oligomers that are readily prepared by this new method.
Organic conjugated materials are useful in an array of applications ranging from photovoltaics to cancer cell imaging.1-3 Interest in these materials stems from the ability to alter the chemical structure to fine tune materials properties.4-7 In addition, the ability to render organic conjugated materials soluble has led to major advances in the field of printed electronics.8 The development of practical organic building blocks and synthetic methods from which to construct organic materials suitable for large scale manufacturing is an active area of study.9-11 With respect to the latter, the direct (hetero)arylation (DHA) reaction has emerged as one of the most useful coupling protocols to make new polymeric and molecular organic materials in a greener fashion.12-15 Direct CH bond functionalization eliminates the need for incorporation of directing groups and allows for previously unavailable substrates to be utilized.
Specifically, for organic materials, their use as active materials in organic solar cells (OSCs) has been widely studied. In this application, the organic materials harvest the energy of photons, create free charge carriers and transport charges to electrodes.17 Within the field of OSCs, the development of non-fullerene acceptors (NFAs) has been of significant recent interest.18-23 
Two classes of NFAs based upon perylene diimides (PDI) and indancenodithiophene (IDT) building blocks have so far emerged as candidates for delivering good performance OSCs. The IDT based NFAs have an IDT core flanked with planar, electron withdrawing end caps, with the entire molecule rendered electron accepting.24,25 The IDT core is insulated with bulky side chains and serves to shuttle electrons within the molecule, while the endcaps drive self-assembly and facilitates electron transfer. The molecules typically adopt a very planar geometry.
In contrast, PDI-based NFAs are multi-chromophore in nature and the best performing materials have highly twisted geometries to prevent strong aggregation of the PDIs, allowing for appropriate phase separation within the active layer films.26-28 Many of the better performing materials are dimeric in nature, but an emerging trend has been to be construct tetrameric PDI NFAs.29-32 We note in particular that a fused ring PDI-tetramer (FTTB-PDI4) with PDI units ring-fused to a tetrathienylbezene is currently the best performing material to our knowledge.45 
U.S. Pat. No. 9,865,819 relates to certain nitrogen annulated perylene diimides useful as electron transport materials in organic electronic devices. In one aspect, the patent relates to N-annulated PDI compounds of formula:
where:X is halogen (F, Cl, Br or I), triflyl, tosyl, or mesyl;R1 and R2 are independently straight-chain or branched alkyl groups having 1-30 carbon atoms; andR3 is a straight-chain or branched alkyl group having 1-30 carbon atoms. These compounds are at least employed to prepare PDI dimers of formula:

The patent also relates to PDI dimer compounds of formula:
where M is certain divalent linking moieties selected from an arylene, a heteroarylene, an alkynylene, a dialkynlyene, an organic dye or M is and
where M1 is arylene, a heteroarylene, or an organic dye molecule, and to compounds of formula:
where:p is 0 or 1, n is 2, 3 or 4, and M1 is arylene, a heteroarylene, or an organic dye molecule and M 1 groups do not contain thiophene groups. This patent is incorporated by reference herein in its entirety for definitions of groups listed in formulas therein, for methods of synthesis of compounds therein as well as for descriptions of applications of the PDI compounds and descriptions of electronic devices therein.
DHA Reactivity with NPDI-Br:
has been extended with various coupling partners including diketopyrrolopyrrole37,38 (DPP), isoindigo37 (II), thienyl isoindigo37 (II-TH), squaraine39, and thieno[3,4-c]pyrrole-4,6-dione (TPD)40. The inventors are not aware of any report of using DHA for couplings with IDT.
PDI and IDT coupling via Stille coupling have been reported previously and to require silica-gel column chromatography purification.34-36 The PDI dimer, IDT-2PDI:
was reported prepared in 78% yield by reaction of the trimethyl tin IDT derivative:
with 2× of the PDI starting material:
with Pd(PPh3)4 in toluene (110° C.)34. The structurally related PDI dimer:
was reported prepared by an analogous method.35 
PDI Dimers of Formula:
where:X is C or N and R1 is 2-ethylhexyl are reported by Chang et al.36 References 34, 35 and 36 are each incorporated by reference herein in its entirety herein for description of methods for characterization of materials and preparation of electronic devices using these materials.
CN107286157 published Oct. 24, 2017 appears to report the synthesis of certain PDI tetramers having a core of 3,3′-bithiophene of structure:
where R is various branched alkyl groups. The document also includes tetramers of structure:
where:n is 0, 1 or 2; R is an alkyl with 5-30 carbon atoms, R′ is H or an alkyl with 1-15 carbon atoms and X is H, CN or alkoxy having 1-10 carbon atoms. Tetramer cores:
are more specifically described therein. This document is incorporated by reference herein in its entirety for descriptions of various tetramers and for support for optional exclusion of certain cores from claims herein.
This invention extends the DHA coupling method to reaction of N-annulated PDI derivatives and related PDI derivatives with certain thiophene-based cores, such as IDT, to prepare new N-annulated PDI tetrameric, hexameric, octameric and higher oligomeric structures. The resulting PDI tetramers and higher oligomers function as non-fullerene acceptors providing OSCs with high open-circuit voltages preferably greater than 1V.